Molecular tools to investigate sharka disease in prunus species

Sharka, a virosis that affects the most important fruit species belonging to the Prunus genus, is a major disease whose consequences heavily impact stone fruit production. Despite many decades have passed since the disease was first reported and its etiological agent, the potyvirus-type Plum Pox Virus, was recognized as the causative agent, the mechanism of its virulence still remains unclear. The virus is propagated by both its natural insect vectors, mainly aphids and by agronomical practices like the propagation through infected material. The diffusion of the disease can only be attained through removal of infected plants in the orchards, provided that appropriate early diagnostics measures are adopted. A second measure of intervention is provided by the control of aphid populations in the orchards although this seems to be a time-limited strategy. A third strategy is represented by the cultivation of plant material featuring inborn resistance to the virus. Although this seems the most appropriate way to address the problem, it is of limited applicability. In fact, while in some Prunus species, like apricot, there is evidence of some type of resistance, no clear sources of resistance are known for others like peach or plum. A fourth strategy is represented by transgenesis, provided that solid sources (genes) of resistance are identified and transformation and regeneration protocols are available. While this seems to be the most promising way, in the medium term, its applicability is still limited by public and political acceptance of the transgenic approach. Various programs are underway to investigate the type of resistance and the factors involved. In this review we address the various aspects of the investigation on PPV and its control which encompass the genetics and the physiology of plant-virus interaction, the identification of candidate genes to be used to limit its infection and spread, the most modern ways to early diagnose the infection and the cutting-edge approaches of gene silencing.